In situ combustion technique



Nov. 7, 1961 F. E. FREY 3,007,520

IN SITU COMBUSTION TECHNIQUE Filed Oct. 28, 1957 Io INJECTION IGNITION BOREHOLES) BOREHQLE AIR IN l4 I4 AIR IN Y) b AIR INJECTION BOREHOLE lNJECTiON BOREHOLE PRODUCTION WELL I} ,PRODUCING,: {I STRATUM l1 Iii l: B]

'coMBusT IbN ZONE INVENTOR. F. E. FREY FIG. 2. 3, 4 m;

ATTORNEYS.

United States Patent 3,007,520 IN SITU COMBUSTION TECHNIQUE Frederick E. Frey, Bartlesviile, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Oct. 28, 1957, Ser. No. 692,641 16 Claims. (Cl. 166-11) This invention relates to a process for initiating in situ combustion in a stratum containing carbonaceous material and to a process for the recovery of hydrocarbons from such a stratum.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades most of the remaining hydrocarbon material. One of the problems involved in the recovery of hydrocarbons by in situ combustion lies in the difficulty in initiating combustion of the carbonaceous deposit in the stratum. Usually the section of the stratum adjacent an ignition borehole is heated for an extended period, such as several days or even weeks, so as to raise the temperature of the section of stratum to a combustion supporting temperature for the carbonaceous material therein and while the stratum is at this temperature air or other oxygen containing gas is injected into the stratum so as to initiate combustion of the carbonaceous deposit.

An object of the invention is to provide an improved process for the production of hydrocarbons by in situ combustion in a stratum containing carbonaceous material. Another object is to provide an improved process for initiating combustion in a carbonaceous stratum. A further object is to provide a process for initiating in situ combustion which requires a minimum of time. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

Because carbon monoxide and oxygen are more sus ceptible to catalysis than hydrocarbon material and oxygen, the catalytic oxidation of carbon monoxide within a stratum containing carbonaceous deposits is an eifective and efiicient means of heating a stratum containing car- .bonaceous material to a combustion supporting temperature so that merely contacting the hot stratum with an oxygen containing gas initiates the combustion of carbonaceous material. Accordingly, a broad aspect of the invention comprises catalytically oxidizing a mixture of CO and O in contact with a section of a carbonaceous stratum adjacent an ignition borehole therein so as to heat said section and the carbonaceous material therein to a combustion supporting temperature and, while hot or at combustion supporting temperature, increasing the oxygen concentration in the hot area either by cutting otf the flow of CO or by increasing the proportion of oxygen being fed to the area so that more than the required amount of oxygen is present to oxidize CO to CO thereby initiating combustion of the carbonaceous material and consequently establishing in situ combustion in the stratum.

A preferred method of operation comprises injecting a mixture of CO and 0 thru a plurality of boreholes surrounding an ignition borehole and forcing the injected mixture thru the stratum toward the ignition borehole so that the oxidation of CO is catalyzed by the natural minerals in the stratum and the resulting oxidation raises the temperature of the stratum to a combustion supporting temperature for the carbonaceous material in the stratum as the oxidation is continued. The injection ice boreholes are spaced radially at a distance from the ignition borehole in the range of about six inches to several feet. 'It is feasible by modern drilling techniques to drill the injection boreholes thru the ignition borehole by directional drilling, or oriented directional drilling, which are conventional drilling techniques. Another technique comprises injecting the oxygen containing gas or the carbon monoxide thru the stratum toward the ignition borehole from one or more injection points and contacting the injected gas at the wall of the ignition borehole with the other gas so as to cause oxidation of the carbon monoxide adjacent the wall of the borehole and thereby heat the section of the stratum adjacent the borehole to combustion supporting temperature for the carbonaceous material in the stratum. It is also feasible to inject a mixture of carbon monoxide and oxygen into the stratum directly from the ignition borehole to eifect the heating thereof preliminary to starting in situ combustion of the carbonaceous material.

In relatively deep wells where the temperature is F. or higher the catalytic action resulting from minerals found in the formation causes combustion of carbon monoxide in air within the formation without adding heat thereto. In instances Where the formation is at lower temperatures, the temperature of the injected air or gaseous mixture of air and carbon monoxide can be raised to such a level that combustion of the CO is efiected upon contacting of the mixture with the formation minerals. Such minerals as iron oxide and even clay and silica catalyze the reaction of CO with 0 Where the catalytic activity of the minerals in the formation is insuflicient to catalyze the reaction of CO with 0 at low temperatures, it is feasible to introduce etiicient oxidation catalysts to the stratum thru the ignition borehole and/ or thru injection boreholes spaced therefrom. A preferred method comprises packing a section of the ignition borehole adjacent the carbonaceous-bearing stratum with a strong oxidation catalystrand effecting the mixing of CO and O in the borehole in contact with the catalyst and particularly along the wall of the borehole so as to heat the same to the required combustion supporting temperature.

Catalysts such as the oxides of Cu, V, Fe, Ni, Co, Mn, and Ag induce combustion of CO at relatively low temperatures, well below 150 F. Finely divided Pt and Pd have a similar catalytic activity. Other catalysts effect tthe oxidation of CO and CO in the presence of oxygen at atmospheric temperature and even as low as 32 F. Such catalysts include mixtures of CuO and MnO AgO and MnO CuO and Fe O and MnO with one of the higher oxides of nickel, cobalt, or iron. All of these mixtures are even more effective if a small amount of ceria up to 1 or 2 percent by weight is incorporated therein. The catalytic effect is also enhanced by incorporation in the mixture of a small amount up to two weight percent of finely divided Pt, Pd, or Ag, or mixtures thereof. A specific highly eifective catalyst even at freezing temperatures (32 F.) is Hopcalite which comprises a mixture of cupric oxide, manganese dioxide, cobaltic oxide, and silver oxide preferably in the propor= tions in weight percent of 30, 50, 15, and 5, respectively. Another effective catalyst consists of a mixture of manganese dioxide and cupric oxide which has incorporated therein any one of ceria, cobaltic oxide, or a reduced fine- 1y divided platinum metal. Of course, it is to be understood that any elfective oxidation catalyst may be utilized in the process.

After the temperature of the stratum surrounding the ignition borehole has been raised to combustion supporting temperature for the in-place carbonaceous material, which is in the range of about 450 to 600 F. or more, depending upon the pressure and the concentration of O in the oxygen containing combustion supporting gas, combustion can be readily initiated by direct injection of oxygen-containing gas thru the ignition borehole. A preferred technique comprises injecting combustion supporting gas into the hot stratum from one or more boreholes surrounding the ignition borehole and closely spaced therefrom so that ignition of the carbonaceous material in the stratum in the heated area thereof is effected immediately upon contact with the injected air and a combustion zone is established in the stratum between the injection boreholes and the ignition borehole. Where the injection boreholes are spaced within six inches to several feet of the ignition borehole, the driving of the combustion zone thru the stratum can then be readily effected by injecting air or other combustion supporting gas, such as oxygen-enriched air or substantially pure thru injection boreholes spaced considerably more remote from the ignition borehole than the closely spaced injection boreholes. These more remote injection boreholes may be spaced from 50 feet to one-quarter or even one-half mile from the ignition borehole.

When utilizing inverse air injection to move the cornbustion front thru the stratum, combustion gases and produced hydrocarbons pass thru other production wells and are recovered therefrom by conventional means. When the combustion front is moved thru the stratum by air injection thru the ignition borehole, combustion gas and produced hydrocarbons are removed from the formation thru the remote boreholes. When utilizing inverse air injection to feed the combustion zone, it is also feasible to recover produced hydrocarbons and combustion gases from the injection boreholes spaced closely around the ignition borehole.

A more complete understanding of the invention may be had by reference to the accompanying drawing of which FIGURE 1 is a plan view of a borehole spacing and arrangement for effecting the process of the invention; and FIGURE 2 is an elevation thru a section of a stratum showing a preferred arrangement of apparatus and borehole spacing for operating in accordance with the invention.

Referring to FIGURE 1, an ignition borehole is surrounded by closely spaced injection boreholes 12 in a conventional five spot pattern and these are surrounded by more remote injection boreholes 14 in a similar pattern. When utilizing direct injection of air thru ignition borehole 10, boreholes 14 become producing boreholes. Other patterns utilizing fewer or a larger number of boreholes may be utilized in practicing the invention.

In FIGURE 2, ignition borehole 10 is provided with production or injection tubing 16 which may be perforated opposite producing stratum 18 when utilized for injecting CO and/ or air. Closely spaced injection borehole 12 is provided with valved conduits 20 and 22 for injection of air and CO. More remote borehole 14 is provided with valved conduit 24 for air injection and, when these boreholes are utilized as production boreholes, conventional production tubing is introduced thereto.

Utilizing the arrangement of boreholes and equipment shown in FIGURES 1 and 2 in accordance with a preferred embodiment of the invention air and C0 are injected into borehole 12 thru conduits 20 and 22 and the resulting mixture is forced thru permeable stratum 18 toward borehole 10 and the minerals in the stratum and/ or a catalyst bed in borehole 10 catalyze the oxidation of CO to CO thereby heating up the stratum between ignition borehole 10 and injection boreholes 12 to a combustion supporting temperature such as about 600 F. While the stratum in this area is at said temperature, the flow of CO into borehole 12 is cut off and air entering the stratum in the heated area ignites the carbonaceous material therein and establishes an in situ combustion zone in an annular ring around ignition borehole 10. The temperature of this combustion zone is usually in the range of about 1000 to 1500 F. so that the temperature thereof remains at a combustion-supporting level while air injected thru conduit 24 and borehole 14 is passing thru stratum 18 to the combustion zone around borehole 10. During this inverse air injection step, the injection of air thru borehole 12 is cut off and gases and liquids driven from the formation of the flow of inverse air may advantageously be removed from borehole 12. When inverse air arrives at borehole 12, conduits 20 and 22 are closed so that air penetrates the hot zone surrounding borehole 10 and continues the combustion of carbonaceous deposits and the combustion zone is moved thru the stratum toward more remote boreholes 14 as shown at 26. This combustion zone 26 is shown continuous vertically over substantially the thickness of stratum 18. Continued injection of air thru boreholes 14 moves the combustion zone thru the stratum to these injection boreholes and after .arrival thereof, if injection of air is continued, the combustion zone is reversed and moves back thru the stratum to the ignition point around borehole 10, feeding upon the carbonized deposit left in the stratum by the first burning phase.

In accordance with another procedure, particularly where the distance between ignition borehole 10 and boreholes 12 is several feet, initiation of in situ combustion may be readily effected by injecting air into the stratum thru conduits 16 in borehole 10, while the adjacent stratum is at combustion temperature, and after a combustion zone several inches thick, radially, and extending continuously along the borehole wall within said stratum, has been established around borehole 10, the injection of air thru conduit 16 can be terminated and injection of air thru boreholes 12 resumed so that the combustion zone is moved toward boreholes 12 by inverse air injection therethru. Continuation of air injection thru borehole 12 after the combustion zone reaches these boreholes drives the combustion front toward more remote boreholes 14-, providing borehole 10 is sealed. However, it is preferred to advance the combustion zone thru the stratum by inverse air injection thru the more remote boreholes.

When mixing CO and oxygen, or air, prior to injecting the mixture into the formation, it is preferred to maintain the concentration of CO in the range of 1 to 13 percent as such mixtures can be used without danger of flame propagation which is impossible under these conditions.

The CO for the process may be obtained from any source, such as from the incomplete combustion of hydrocarbon material. Burning hydrocarbon material with less than the stoichiometric amount of oxygen to form CO produces an abundance of CO under properly controlled combustion conditions. The resulting gas may be injected into the formation while hot and there contacted with air injected thru another borehole so as to facilitate the combustion of CO. However, it is not necessary to inject the CO-containing gas in hot condition, and in most instances it is desirable to cool the combustion gas to condense water therefrom prior to injecting the CO into the formation or prior to mixing the same with air for injection into the stratum.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A process for producing hydrocarbons from a stratum containing combustible carbonaceous material and oxidation catalyst which comprises injecting a mixture of free-oxygen-containing gas and CO in which the CO is in a concenration in the range of l to 13 mol percent into said stratum thru a plurality of injection boreholes therein surrounding a central ignition borehole and spaced therefrom a distance in the range of 6 inches to several feet and passing said mixture thru said stratum to said central borehole so that said mixture passes thru the entire wall of an elongated section of said ignition borehole; maintaining the temperature of said wall at least F.

so that catalytic oxidation of CO to CO is efifected thereby heating said wall to combustion supporting temperature of said carbonaceous material; while said wall is at said temperature cutting oil the injection of CO and continuinig inverse injection of said free oxygen so that the hot wall is contacted with said oxygen-containing gaswhereby combustion of carbonaceous material over said entire wall is effected and the resulting combustion zone is advanced radially outwardly from said central ignition borehole toward said injection boreholes; and recovering hydrocarbons driven from said stratum by said combustion thru said central ignition borehole.

2. The process of claim 1 wherein injemion of oxygencontaining gas thru said injection boreholes is discontinued and injection of said gas thru a series of more remote boreholes is effected when said combustion zone approaches said injection boreholes.

3. The process of claim 1 wherein said free-oxygencontaining gas is air.

4. The process of claim 1 wherein said free-oxygencontaining gas consists essentially of O 5. The process of claim 1 wherein said free-oxygencontaining gas is O -euriched air.

6. A process for initiating in situ combustion continuously along an elongated section of an ignition borehole within a carbonaceous stratum containing catalytic material which comprises injecting a mixture of and CO, in which the CO is in the range of 1 to 13 mol percent, thru an injection borehole in said stratum so as to cause said mixture to pass radially from said borehole thru said stratum and thru the wall of an elongated section of an ignition borehole in said stratum ofifset from saidinjection borehole a distance in the range of 6 inches to several feet, the temperature of the wall of said section of borehole being at least 150 F. whereby said CO is catalytically oxidized to CO and said wall is heated to a combustion supporting temperature of said stratum in contact with O and while at said temperature contacting the resulting hot wall with combustion-supporting gas containing free 0 so as to ignite the carbonaceous material along said section of borehole.

7. The process of claim 6 wherein the ignition of said carbonaceous material is eflected by terminating the injection of said mixture and contacting said hot wall with said combustion-supporting gas.

8. The process of claim 7 wherein said combustion supporting gas is air and same is injected thru said injection borehole; continuing the injection of air thru said injection borehole so as to cause a combustion zone to move countercurrently to air flow to said injection borehole with egress of produced fluids thru said ignition borehole; and, as said combustion zone arrives at said injection borehole, shutting in said ignition borehole, discontinuing injection of said combustion-supporting gas thru said injection borehole, injecting last said gas thru a second injection borehole offset from first said injection borehole a substantially greater distance than first said distance so as to move said combustion zone toward said second injection borehole; and recovering fluids produced during injection thru said second injection borehole, thru said first injection borehole.

9. The process of claim 6 wherein an oxidation catalyst is introduced to said ignition borehole to supplement natural catalytic action of stratum constituents.

10. The process of claim 9 wherein said catalyst comprises manganese dioxide.

11. The process of claim 9 wherein said catalyst comprises vanadium oxide.

12. The process of claim 9 wherein said catalyst comprises iron oxide.

13. The process of claim 9 wherein said catalyst comprises MnO in admixture with at least one member of the group consisting of the oxides of Cu, Ag, Ni, Co, and Fe, said catalyst containing ceria in an amount up to 2 weight percent of the catalyst.

14. A process for initiating in situ combustion in a permeable stratum containing combustible carbonaceous material which comprises catalytically oxidizing CO with free-oxygen-containing gas in contact with an elongated section of said stratum along an ignition borehole there in so as to heat said section to combustion supporting temperature of said material; While said section is at said temperature, terminating CO oxidation and injecting air thru said stratum from at least one oflset borehole therein and into said section so as to ignite and burn the carbonaceous material therein thereby establishing inverse in situ combustion in said section of stratum.

15. The process of claim 14- wherein said oxygen-containing gas is injected into said stratum thru said at least one borehole; said at least one borehole is spaced from said ignition borehole a distance in the range of 6 inches to several feet; and said gas is passed laterally thru said stratum to said ignition borehole and said CO is injected into said ignition borehole so as to burn same adjacent the wall thereof.

16. The process of claim 15 wherein said CO is supplied in a hot stream of gas resulting from incomplete combustion of a hydrocarbon with oxygen.

References Cited in the file of this patent UNITED STATES PATENTS 2,382,471 Frey Aug. 14, 1945 2,722,277 Crawford Nov. 1, 1955 2,793,696 Morse May 28, 1957 2,804,146 Crawford Aug. 27, 1957 2,901,043 Campion et a1 Aug. 25, 1959 

